The rare flavour-changing neutral current decays of the B mesons are among the most sensitive laboratories to probe the Standard Model and indirectly search for physics beyond it. In this report, a complete review of the analyses of the rare $b\to s\ell\ell$ decays performed by the CMS Collaboration is presented. In particular, three decays have been studied: $B^0\to K^{*0}\mu\mu$, $B^+\to K^+\mu\mu$, and $B^+\to K^{*+}\mu\mu$. Finally, the projection of the analysis of the $B^0\to K^{*0}\mu\mu$ decay channel to the HL-LHC data-taking is presented.